Dual-Band, Differentially-Fed Filtenna With Wide Bandwidth, High Selectivity, and Low Cross-Polarization

Abstract

A compact dual-band, differentially fed filtenna with wide bandwidth, high selectivity, and low cross-polarization is presented. It is composed of a slot-loaded rectangular patch, two pairs of shorting pins, a pair of novel differential coupling feedlines, and a defected ground structure (DGS). Good broadside radiation patterns with an adjustable frequency ratio (FR) between its two bands are realized. A pair of U-shaped slots is loaded on the patch to enhance the bandwidth of the lower passband. The DGS and its compact differential feedlines produce five out-of-band radiation nulls to improve the frequency selectivity of the two passbands. Simultaneously, extra in-band resonances are introduced that broaden the impedance bandwidth while maintaining a compact <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.155\lambda _{0}^{2}$ </tex-math></inline-formula> aperture size and a relatively low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> height). Prototypes were fabricated, assembled, and tested. The measured results, in agreement with their simulated values, demonstrate that it exhibits −10 dB fractional impedance bandwidths of 17.5% and 8.2%, peak realized gain values of 8.4 and 9.5 dBi, and cross-polarization levels smaller than −44 and −40 dB, in its lower and upper passbands, respectively. Its dual-band quasi-elliptic responses have sharp roll-off rates and high stopband suppression levels.